1. Field of the Invention
Apparatus and methods consistent with the present invention relate to encoding and decoding a multi-view image, and more particularly, to encoding and decoding a multi-view image, in which display quality degradation can be prevented for an image at any view.
2. Description of the Related Art
In multi-view image encoding, images input from a plurality of cameras that provide a multi-view image are simultaneously encoded. The multi-view image is compression encoded using temporal correlation and inter-view spatial correlation.
FIG. 1 illustrates image sequences of a multi-view image according to the related art.
In FIG. 1, a horizontal axis is a time axis and a vertical axis is a view axis. In multi-view image encoding, an intra (I) picture is periodically generated for an image at a base view and temporal prediction or inter-view prediction is performed based on generated I pictures, thereby predictive-encoding other pictures. An arrow direction indicates a direction in which reference is made for prediction.
Temporal prediction is performed using temporal correlation between images at the same view, i.e., in the same row. Inter-view prediction is performed using spatial correlation between images at the same point of time, i.e., in the same column.
In FIG. 1, each row shows an image sequence at each view for a multi-view image over time and each column shows an image sequence at views 0, 1, 2, through to 7, sequentially from top to bottom. The view 0 is a base view and an image sequence 110 in the first row is at the base view. Pictures included in the image sequence 110 at the base view are predictive-encoded using only temporal prediction without using inter-view prediction.
Each column shows multi-view images at the same point of time. Pictures included in columns 130, 140, and 150 in which an image at the base view is an I picture are referred to as anchor pictures. The anchor pictures are encoded using only inter-view prediction.
Referring to FIG. 1, I pictures periodically exist in the image sequence 110 at the base view, but no I picture exists in image sequences 120 at other views. In other words, I pictures periodically exist only in positions corresponding to anchor pictures in the image sequence 110 at the base view.
According to the related art, since image sequences 120 at views other than the base view are predictive-encoded without using an I picture, they are likely to suffer from display quality degradation when compared to the image sequence 110 at the base view. Even if spatial correlation between cameras, i.e., inter-view spatial correlation, exists, prediction is performed without using an I picture for an image at each view. As a result, prediction is likely to be inaccurately performed and thus display quality degradation is likely to occur.
FIG. 2 illustrates syntax of a sequence parameter of a multi-view image according to the related art.
First, information about the number of views of a multi-view image, i.e., ‘num_views_minus—1’, is set. Once ‘num_views_minus—1’ is set, information about the number of views that are referred to by each view for inter-view prediction, i.e., ‘num_multiview_refs_for_list0[i]’ and ‘num_multiview_refs_for_list1[i]’, is set. ‘list0’ is a list of reference views whose numbers are less than the current view number from among all reference views referred to by the current view, and ‘list1’ is a list of reference views whose numbers are greater than the current view number from among all the reference views.
Once the number of reference views referred to by each view is set, information indicating each view refers to which view is set in detail. At this time, since a view referred to by an anchor picture and a view referred to by a non-anchor picture are different from each other, the information is set separately for the anchor picture and the non-anchor picture. All parameters set in this way are encoded and then inserted into a bitstream.
As illustrated in FIG. 1, in a multi-view image, reference views referred to by pictures at each view for inter-view prediction do not change over the entire image sequence. For example, referring to FIG. 1, in an image sequence at view 2, i.e., in the third row, anchor pictures in columns in which I pictures exist are predictive (P) pictures and refer only to the view 0 and non-anchor pictures do not refer to any view. The reference view referred to by the view 2 does not change over the entire image sequence. Similarly, in an image sequence at view 3, i.e., in the fourth row, anchor pictures and non-anchor pictures refer to views 2 and 4 and the reference views referred to by the view 3 do not change over the entire image sequence.
Thus, when a reference view does not change, information about a reference view referred to by each view in a multi-view image for inter-view prediction may be set as illustrated in FIG. 2. However, when information about a reference view changes in an image sequence, it cannot be expressed properly with the syntax illustrated in FIG. 2.